Coated paper



Patented Oct. 27, 1942 UNITED STATES PATENT OFFICE COATED PAPER Frank R. Stoner, Jr., and Daniel M. Gray, Sewickley, Pa., assignors to Stoner-Mudge, Inc.,

Pittsburgh, Pa., a. corporation of Pennsylvania No Drawing. Application March 11,1942,v Serial No. 434,252

8 Claims.

ford a film that is stable against the oxidative influence of the atmosphere, and against penetration by moisture, by acid and alkaline vapors such as sulphur dioxide, hydrogen sulphide, and ammonia (which may and usually do have deleterious effect upon dyes and pigments of printed paper, if the paper be printed), and stable with respect to commodities to which the'paper may be applied as a wrapper. It should be resistant to penetration by oil and grease; The finishing varnish should contain no substances that are varnish. The varnish is applied, typically, by

roll-coating in a paper-coating machine, or it may be knifed on. Thereafter, the varnished paper is brought to an elevated temperature for a short time, usually not exceeding several minutes, to drive off the varnish solvent, to oxidize or polymerize the incompletely reacted compounds in the varnish, if such be present, and to secure an adequate degree of adhesion of the applied varnish to the underlying paper.

There are certain well-defined limitations on the type of materials suitable for producing finishing varnishes. Because of the thermally unstable nature of paper, subject as it is to loss of normal moisture content, consequent embrittlement, and eventual decomposition as temperature rises, it is necessary that the baking or curing schedule for the varnish when applied be short, not exceeding several minutes in length, and that the baking temperature be as low as possible, not exceeding 300-600 F. (the permissible peak varying with the quality and character of the paper, even though the time of exposure to such temperature be no longer than 30 seconds). Accordingly, the finishing varnish must yield a completely tack-free and dry film, free of entrapped solvents, of incompletely reacted constituents, and of reaction byproducts, when baked on schedules not exceeding 300-600 F. for 30-60 seconds. In addition, the resulting baked-out film of finishing varnish must be essentially colorless and should preferably have high gloss; for many purposes it must be odorless and tasteless; it must be adequately adhered to the paper; it must be sufiiciently flexible to withstand bending and folding without cracking or breaking loose from the underlying paper; and it must be sufiiciently tough and mar-resistant to withstand the usual abrasive actions and rubbings that are encountered in subsequent application and use of the coated paper, such applications and uses, for example, as the pasting of labels to containers and the wrapping of packages of bread, soap, and other commodities. Another requirement of a satisfactory finishing varnish is that it shall afthemselves harmful to the sensitive dyes and pigments in the printing inks (if the paper he printed), nor to the wrapped commodities; it should yield a film that is stable against degradation by actinic light; it should not become opaque, nor develop any color in the absence of light, or on aging. Finally, in its application, there should be very little, if any, penetration into the paper: the film, rather, should lie as a continuous and discrete layer upon the paper.

We have characterized thev product of our invention as sheeted cellulosic material coated with a finishing varnish; and we have taken, by way of example, a very hard-textured semi-transparent paper stock. We include within the term sheeted cellulosic material sheeted cellulose fibrethat is to say, paper-whether the constituent fibre be unmodified or modified, and we include in the term sheeted cellulose acetate and regenerated cellulose. Specifically,, we have found industrial use for hard-textured paper, particularly that hard-textured thin and semitransparent paper known as glassine, as well as paper heavily sized with familiarclay-rosin size, when coated with the varnish of the composition and affording the attributes herein specified. Even in the case of reasonably hard-textured paper stock bearing upon its surface designs and lettering in suitable printing inks consisting essentially of natural or synthetic resins, together with drying oils and modifying agents, in and of themselves colorless, but colored by addition of pigments and dyes, and adapted to service in such manner as the art knows, and transferred to thepaper from suitable printing rolls-even in this case we find that the paper coated over its inkbearing surface with the varnish of the composition herein specified manifests integrity of union together with the attributes specified above that render it superior in service.

It is the object of our invention to produce sheeted cellulosic material coated with a finishing varnish that shall possess the desirable properties specified above, and, notably, superior adhesion of the varnish to the sheet and resistance to abrasion and scufiing. This article must be produced without the necessity of resorting to the extreme baking temperatures usually required for setting chemically resistant varnishes. The finishing varnish that we employ lends itself advantageously to heat-sealing operations, with or without application of such adhesives as usually are employed for the purpose.

We have found that the above objects may beattained in high degree by employing as the fihn-forming components of our finishing varnish a mixture of (1) a copolymer of vinyl halide and a vinyl ester of a lower aliphatic monocarboxylic acid, and (2) a copolymer of a vinyl halide, a vinyl ester of a lower aliphatic monocarboxylic acid, and maleic acid, maleic anhydride, or a lower alkyl ester of maleic acid.

For convenience, the term lower will be used throughout the specification and claims to designate aliphatic radicals containing no more than 6 carbon atoms. Thus, by vinyl ester of a lower aliphatic monocarboxylic acid" we mean vinyl acetate, vinyl propionate, vinyl butyrate', and the higher aliphatic homologs containing up to 6 carbon atoms in the alkyl group attached to the esterifying carboxyl group. By lower alkyl esters of maleic acid we mean the methyl, ethyl, propyl, butyl, and higher homologous alkyl esters of maleic acid containing up to 6 carbon atoms in the esterifying alkyl groups.

The polymers and copolymers of vinyl halides and vinyl'esters are well known. They result from the conjoint polymerization of a vinyl halide, typically vinyl chloride, with a vinyl ester of a lower aliphatic monocarboxylic acid, typically vinyl acetate, usually in the presence of a suitable solvent for the monomeric starting materials, and a peroxide catalyst. We have found that the copolymers of vinyl chloride and vinyl acetate are particularly suited for our purposes as component 1, and we advantageously employ copolymers in which the percentage of vinyl chloride lies between 65% and 95% by weight, the percentages of vinyl acetate being correspondingly 35% and Several preferred compositions for component 1 are as follows:

Per cent by weight (a) Vinyl chloride 80 Vinyl acetate 20 (17) Vinyl chloride 87 Vinyl acetate 13 (c) Vinyl chloride 92 Vinyl acetate 8 For convenience we shall hereafter refer to these copolymers which form our component 1, as vinyl halide-vinyl ester copolymers."

The mixed copolymers of vinyl halides, vinyl esters of lower aliphatic monocarboxylic acids, and maleic acid derivatives, which we use as our component 2, are not so widely known. They result from the conjoint polymerization of vinyl halides and the previously described lower aliphatic vinyl esters, together with a minor proportion of maleic acid, maleic anhydride or a lower aliphatic ester of maleic acid. (A typical copolymer involving only vinyl chloride and maleic aliphatic esters is described in United States Letters Patent 2,187,817, for example.) We have found that copolymers of vinyl chloride, vinyl acetate, and maleic anhydride are particularly suitable for our component 24, though we may advantageously employ copolymers containing maleic acid and lower aliphatic maleic esters in place of the maleic anhydride. We have found it desirable to employ copolymers in which the percentage of vinyl chloride lies between 65% and 99% by weight, the remainder being vinyl acetate and maleic derivative. Thus the percentage of vinyl acetate will be reduced by the amount of maleic derivative present, which will ordinarily lie between 0.2% and 5.0% by weight, based on maleic anhydride. By simple molecular weight ratios it is obvious that a maleic content of 1%, based on the anhydride, is equal to 1.18% of maleic acid, to 1.33% of ,monomethyl maleic ester, to 1.47% of dimethyl ester, to 1.47% of monoethyl ester, and to 1.76% of diethyl ester, for example. Throughout the .specification and claims, it will be understood Per cent by weight (d) Vinyl chloride 85.0 Vinyl acetate 13.0 Di-methyl maleic ester 2.0

(e) Vinyl chloride 70.0 Vinyl acetate 28.7 Maleic anhydride 1.3

(f) Vinyl chloride 65.0 Vinyl acetate 34.2 Maleic acid 0.8 (9) Vinyl chloride 87.0 Vinyl acetate 11.8 Maleic anhydride 1.2

For convenience we shall hereafter refer to these maleic-modified copolymers which form our component 2, as maleic-modified vinyl halide-vinyl ester copolymers.

It is important that the degree of polymerization of the copolymers of components 1 and 2 be controlled within fairly close limits. The degree of polymerization may not be too low, to the end that unstable, brittle, relatively soft and pervious copolymers be not formed; the degree of polymerization may not be too high, to the end that insoluble or only sparingly soluble, rubbery, non-adherent copolymers be not formed. We advantageously employ copolymers having molecular weights in th'e'range of 5,000 to 20,000 as determined by the familiar Staudinger viscosity method, and prefer to employ these in the range of 8,000 to 14,000. Our preferred materials have absolute viscosities as shown in the accompanying table, determinedon 18% solutions in pure methyl isobutyl ketone.

Absolute viscosity Resin component range C'mti no at We.

forts proved useless, inthat such elevated temperatures were more destructive of the underlying paper and even of the unmodified vinyl resin film, than could be compensated for by the accompanying improvement in adhesion.

In an effort to improve the degree of adhesion, we have experimented widely. Various admixtures with other resins compatible with the vinyl halide-vinyl ester resins were tried. Thus we have employed admixtures with oil-modified and non-oil modified polybasic acid polyhydric alcohol resinoids familiarly known as alkyds, nitrocellulose and other cellulose esters such as cellulose acetate, cellulose acetate-propionate, and cellulose acetate-butyrate, ethyl cellulose, various natural and synthetic compatible waxes, phenol-aldehyde condensation products, and the like. While the degree of adhesion was in a few cases slightly improved by the addition of these substances, the improvement was in no case of sufficient magnitude to have commercial possibilities; or, if so, other undesirable qualities such as decreased scuff resistance, decreased hardness and decreased flexibility resulted.

Additions of the maleic-modified vinyl halide vinylester copolymers which we previously described and herein specifically disclose as our component 2 showed, however, a spectacular improvement in the degree of adhesion produced. and this without the necessity of increasing the bake temperature and without sacrifice of the other desirable properties associated with vinyl halide vinyl ester films. Our experiments show that blends containing as little as 6% by weight of component 2 give appreciable improvement in adhesion of our finishing varnish film. We find that the percentage of maleic modified vinyl halide vinyl ester constituent may be as great as 50% of the resinous portion without too marked a decrease in the desirable properties of the resulting film. Our preferred composition, however, contains by weight of the maleicmodified vinyl halide vinyl ester component, and 80% of the unmodified vinyl halide vinyl ester component. Higher percentages of component 2 do not appear to give a corresponding increase in adhesion, and the scuif resistance tends to be lowered. Amounts of component 2 less than 20%, while showing improvement in adhesion, are not consistently satisfactory over all hard textured papers. The optimum amount of component 2 appears to be 20%, based on a large number of experiments over various paper stocks, printed upon and unprinted.

Finally, we have attempted preparation of suitable finishing varnishes from maleic-modified vinyl halide vinyl ester copolymers alone. Such varnishes yield films which are unsatisfactory from a commercial standpoint. Stability is poor; scufi resistance is seriously deficient; the moisture resistance is inferior to that of most of the familiar oleoresinous finishing varnishes. It is apparent that only in the blends of our invention are the desirable properties of high degree of adhesion, excellent abrasion and scuff resistance, coupled with inertness to atmospheric oxidation,

acid and alkali resistance, freedom from taste,- odor and color, and moisture impermeability combined. And these properties are obtained in our finishing varnish films employing baking temperatures not exceeding 400 E. for 30 seconds, in contrast to the appreciably more drastic baking schedules necessitated in commercial practice with prior-art varnishes.

The formulation of our improved finishing varnishes offers no difilculty. We prefer to employ lower aliphatic ketones as solvents, typically acetone, methyl-ethyl ketone, methyl propyl ketone, or methyl isobutyl ketone. Other suitable solvents such as butyl acetate, nitroparamns, ethyl ene dichloride, mesityl oxide, or isophorone may -be employed if desired. As diluents we prefer to use the simple aromatic hydrocarbons such as toluol, xylol, and hifiash naphtha. It is advantageous to employ solvent-diluent compositions having relatively low boiling points, in order that complete release of these volatile constituents during the short baking schedule maybe more readily effected. For certain types of application the addition of a plasticizer further to increase the normally satisfactory flexibility of our improved varnish film may be desirable. For this purpose we employ with advantage any of the familiar plasticizers that are compatible with the vinyl resins. Typical of such materials are tricresyl phosphate, dibutyl phthalate, diamyl phthalate, di(butoxyethyl) phthalate, triphenyl phosphate, phenyledixenyl phosphate, castor oil, and the like. is preferably about 25% by weight, based on the total non-volatile content.

The application of our improved finishing varnish to the surface of the paper offers no difliculties. Thus, it may be applied by roll coating on the usual paper coating machines; it may be applied by knifing; and it may be simply brushed,

dipped, or sprayed on. We prefer to bake the so varnished paper for 30 seconds at 365 F. This schedule insures complete removal of volatile solvents and gives improved gloss. Higher baking temperatures are possible, but lead to no useful gain in final properties. Thus we have prepared satisfactory coated glassine, for example, using baking schedules between 20 seconds and 3 min-v Example I Per cent Vinyl chloride 85.0 Vinyl acetate 15.0 (l) Copolymer of- Vinyl chloride 87.0 Vinyl acetate 11.7 7.5

Maleic anhydride 1.3} (2) Copolymer of Methyl ethyl ketone 70.0

Example II Per cent (1) Copolymer-of Vinyl bromide 65.0 Vinyl acetate 35.0} 2) Copolymer of Vinyl chloride 65.0. Vinyl propionate 30.0, 5.7 Diethyl maleic ester 5.0.

Tricresyl phosphate 7.2

Methyl ethyl ketone 63.8

The concentration of plasticizer l Example If! Per cent (1) Copolymer of- Vinyl chloride 90.0} 160 Vinyl butyrate 10.0 (2) Copolymer of- Vinyl bromide 70.0 Vinyl acetate 28.5} 4.0 Maleic acid 1.5 Diamyl phthalate 5.0 Isophorone 7.5 Methyl isobutyl ketone 15.0 Methyl ethyl ketone 7.5 Xylol 45.0

100.0 Example IV Per cent (1) Copolymer of Vinyl chloride 87.0} 180 Vinyl acetate 13.0 (2) Copolymer of- Vinyl chloride 87.0 Vinyl acetate 12.0 2.0 Maleic acid 1.0 Methyl isobutyl ketone 40.0 Xylol 40.0

100.0 Example V Per cent (1) Copolymer of- Vinyl chloride 87.0} 100 Vinyl acetate 13.0 (2) Copolymer of- Vinyl chloride 87.0 Vinyl acetate 11.8 100 Maleic anhydride 0.2 Dimethyl maleic ester--- 1.0 Methyl ethyl ketone 65.0 Cyclohexanone 15.0

100.0 Example VI Per cent (1) Copolymer of Vinyl chloride 87.0} 16') Vinyl acetate 13.0 (2) Copolymer of- Vinyl chloride 87.0 Vinyl acetate 12.0 4.0 Maleic anhydride 1.0 Methyl ethyl ketone 35.0 Toluol 45.0

The percentages by weight of components 1 and 2 based on the total resin content in the 6 examples are given in the following table:

Examples II, III and VI represent preferred compositions; examples I, IV and V are satisfactory but not necessarily preferred.

Having described our invention, and having pointed out the advantages attendant on its use,

We claim as our invention:

1. As an article of manufacture, sheeted cellulosic material coated with a finishing varnish in which the resinous solids consist of (1) ampolymer of vinyl halide and a vinyl ester of a lower aliphatic monoc oxylic acid,'and (2) a copolymer of a vinyl halide, a vinyl ester of a lower aliphatic monocarboxylic acid, and a substance selected from a group consisting of maleic acid, maleic anhydride, and the lower alkyl esters of maleic acid, the article being characterized by superior flexibility, abrasion resistance, and adhesion of the varnish to the cellulosic material, coupled with a high degree of 'inertness to atmospheric oxidation and to attack by oils, grease, and mild alkalis and acids.

2. The article of claim 1 in which the resinous constituents of the finishing varnish consist of (1) 50 to 94 parts by weight of the vinyl halidevinyl ester copolymer, and (2) 50 to 6 parts by weight of the maleic-modified vinyl halide-vinyl ester copolymer.

3. The articleof claim 1 in which the resinous constituents of the finishing varnish consist of (1) 50 to 94 parts by weight of a copolymer of vinyl chloride and vinyl acetate in which the weight percentage of the vinyl chloride lies between 65 and 99, the remainder being vinyl acetate, and (2) 50 to 6 parts by weight of a copolymer of vinyl chloride, vinyl acetate, and a maleic derivative selected from the group consisting of maleic acid, maleic anhydride, and the lower alkyl esters of maleic acid, in which the weight percentage of the vinyl chloride lies between 65 and 99, that of the maleic derivative between 0.2 and 5.0, the remainder being vinyl acetate.

4. The article of claim 1 in which the resinous constituents of the finishing varnish consist of (1) 50 to 94 parts by weight of a copolymer of vinyl chloride (87%) and vinyl acetate (13%), and (2) 50 to 6 parts by weight of a copolymer of vinyl chlorine (87%), vinyl acetate (11.5%), and a substance selected from the group consisting of'maleic acid, maleic anhydride, and the lower alkyl esters of maleic acid (1.5%).

5. The article of claim 1 in which the resinous constituents of the finishing varnish consist of (1) parts by weight of a copolymer of vinyl chloride (87%) and vinyl acetate (13%), and (2) 20 parts by weight of a copolymer of vinyl chloride (87%) vinyl acetate (11.5%) and asubstance selected from the group consisting of of vinyl chloride (87%), vinyl acetate (11.5%), maleic acid, maleic anhydride, and the lower alkyl alkyl esters of maleic acid of 1.5%).

6. As an article of manufacture, a sheet of hard-textured paper coated with a finishing varnish, as defined in claim 1.

7. As an article of manufacture a transparent sheet of glassine coated on at least one side with a non-penetrating, colorless, and transparent finishing varnish, as defined in claim 1.

8. As an article of manufacture a sheet of paper printed upon with resinous printing ink and coated over its printed surface with a finishing varnish, as defined in claim 1.

FRANK R. STONER,'JR. DANIEL M. GRAY. 

